The present invention relates to a refrigeration compressor for use in air conditioning systems for commercial or non-commercial use.
Electric compressors used in air conditioning include those in which the compressor section comprises a reciprocating type, rotary type, or scroll type. These designs are employed in both household and commercial air conditioning equipment. The particular advantages of the various designs in terms of cost and performance are utilized in a growing market.
Regardless of the design, the compressor mechanism and the drive mechanism include sliding elements. Wear and seizing of these sliding elements has significant impact on the service life of the refrigeration compressor. Specific examples of sliding elements having particularly great effect on refrigeration compressor service life are the slide bushing provided between the orbiting scroll of the compressor mechanism and the crankshaft that transmits the rotation of the motor to the orbiting scroll; the Oldham ring used to support the orbiting scroll such that the latter undergoes orbital motion without rotating with respect to the stationary scroll; and a vane, provided to the cylinder, which is in sliding contact with the inside wall of the cylinder and in sliding contact with the eccentrically rotating piston, engaging in follower motion therewith. In the prior art, these sliding elements are fabricated from iron-base sinters in order to improve lubricant retention, and are subjected to quench hardening in order to raise the hardness and improve wear resistance.
Compressors of the prior art, which employ chlorinated refrigerants such as designated CFC R12 and designated CFC R22, exhibit lubricating action produced by the extreme pressure effect of the chlorine contained in the refrigerant, and thus the slide bushing, Oldham ring, and vane present no particular problems in terms of service life, even when used in maintenance-free refrigeration compressors.
It has recently been confirmed that the chlorine atoms contained in the molecules of the designated CFCs damage the ozone layer. The development and use of substitute refrigerants is being planned.
The HFCs (hydrofluorocarbons), which contain no chlorine, are highly serviceable substitutes "Hydraulic Technology '94.6" (published by Nippon Kogyo Shuppan).
However, the fact that these substitute refrigerants contain no chlorine means that the same level of lubricating provided by the conventional designated CFCs cannot be expected. Accordingly, sliding conditions will be more severe, and as long as sliding mechanism design remains unmodified, service life will be shortened. Specifically, wear and seizing of the slide bushing, Oldham ring, and vane will occur. Causes of early wear and early seizing are thought to lie in susceptibility to a critical lubrication state in which portions of the oil film are depleted, due to the inability of the substitute refrigerants to provide lubricating action on par with that of the designated CFCs.
Even where slide bushings, Oldham rings, and vanes are oil-retaining, comprising porous materials produced from sintered metals such as sintered iron containing added Mo and Ni, as taught in Unexamined Patent Application (Kokai) 9-32770, experiments conducted by the inventors indicate minimal improvement in wear resistance when used in conjunction with the substitute refrigerants. Extensive research involving repeated experimentation indicated the following with respect to this point. Firstly, wear resistance is a particular problem at sliding surfaces on which pressure and load are brought to bear; secondly, a possible reason therefor is that the lubricant supplied to the sliding surfaces is induced to penetrate deeply into or is extracted from the cells of the sintered metal due to the action of pressure and load, resulting in early onset of oil film depletion on the sliding surfaces.
In order to examine this point, the inventors of the present invention used a mercury penetration method to conduct a so-called "cell examination" of the cells in sintered metal materials. The test specimens of the prior art used in the tests were an iron-base sintered elements having the composition C: 0.1-1.0 wt %, Cu: 0.5-3.0 wt %, Ni: 1.0-7.0 wt %, Mo: 0.1-1.5 wt %, and subjected to quench hardening. The examination was conducted by ascertaining the amount of mercury penetrating into one gram of the sample material; the penetrating amount corresponds to the total cell volume of the sample. Results are presented in Table 1; total cell volume was 0.0118 cc/g, as ascertained through the corresponding amount of penetrating mercury.
Total Cell Cell Density Volume Prior Art 40-50 .mu.m 7.0 g/cm.sup.3 0.0118 cc/g Specimens
The prior art specimens exhibited density on the order of 7.0 g/cm.sup.3, slightly higher than the usual density of 6.8 g/cm.sup.3 seen in sintered bearings. Various examinations concerning cell condition in the prior art specimens revealed a structure like that modeled in FIG. 3(b). The areas painted out in black are openings a1 to the surface; wide cells a having these openings a1 were present intermittently over the surfaces of the specimens. The size of the wide cells a ranged from 40 .mu.m-50 .mu.m, and these cells were in communication via narrow connecting segments a2 with other cells a having openings on the surface and with other wide cells a without openings on the surface that were interspersed throughout the specimen.
Accordingly, the cells present in the prior art specimens may be accurately termed "open cell". This is consistent with the findings in the examinations that the amount of penetrating mercury is considerable. It is also consistent with the idea that under conditions of pressure and load, large amounts of lubricant penetrate into the surfaces of compressor slide bushings, Oldham rings, vanes, and other sliding elements, causing the oil film to become depleted.
The aforementioned Unexamined Patent Application (Kokai) 9-32770 teaches impregnation of the cells of the sintered iron with a resin in order to prevent the lubricant from escaping into the cells under high loading, which makes it harder for an oil film to form. However, the advantages associated with the lubricant being retained in the cells are lost with this method, and the resin impregnation method entails increased costs.
Unexamined Patent Application (Kokai) 5-33093 teaches the following. Iron-base sintered metals contain residual porosity of 10-20%, but nonetheless possess adequate strength through metal bonding and diffuse bonding among powder grains; the materials also have an oil retaining action whereby the lubricant is retained in the residual cells, so that an oil film forms on mated slide faces during sliding. Exceptional wear resistance and sliding characteristics are thus provided under wet lubrication conditions. However, increased weight is a drawback. A substitute that provides the required strength while retaining wear resistance and sliding characteristics is a quench hardened aluminum alloy powder which is hot cast at a temperature such that the metastable alloy phases of the material are not damaged, and then formed and heat treated to produce a material containing 2-5% 10 .mu.m residual individual cells. The Fe and Ni contained therein form intermetallic compounds with the Al, enhancing high-temperature strength, while the Cu, Mg, and Mn contribute to improved strength, hardness, and other mechanical properties. The residual cells produce an oil retaining action under a wet environment, thereby preventing parts from seizing. Since the residual cells comprise fine closed cells, the material readily withstands stress and resists deterioration at grain boundaries due to penetration by oxidizing atmospheres.
However, sliding elements fabricated from the aluminum alloy powder materials described above cannot be used for the crankshaft that transmits the rotation of the motor to the orbiting scroll of the compressor mechanism, or for the Oldham ring and slide bushing provided between the crankshaft and the orbiting scroll. The reason is that where the sliding elements are fabricated from aluminum alloy powder materials, there is a tendency to experience sticking with the orbiting scroll, which also consists of aluminum-base material. Another reason is that sliding elements constructed from aluminum alloy powder materials tend to have inferior strength to iron-base materials, particularly in the case of small elements like Oldham rings.
Unexamined Patent Application (Kokai) 3-162559 teaches a sliding element consisting of an iron-base material, the surfaces of which are provided with a porous oxide layer, a solid lubricant being retained within this porous oxide layer. Since only the cells of the porous layer are open cell, the problems mentioned earlier are not solved. Experiments conducted by the inventors indicate that the oil film sustaining force achieved with open cells is rather low, at most 100 kgf, as indicated by the black markings in FIG. 7.
Sealing the cells with the solid lubricant does not bring about complete sealing, and thus the open cell morphology is not eliminated, leaving the aforementioned problems unsolved. The sealing treatment also entails increased costs. Another drawback is wearing away of the oxide layer when a maintenance free machine is operated for extended periods or under harsh conditions, resulting in a loss of reliability. The high process temperatures used in oxynitriding of thin films result in deformation of the elements, so that the required precision is not achieved. Accordingly, such methods are unsuitable for Oldham rings.
Unexamined Patent Application (Kokai) 54-13005 teaches the following with regard to metal sinter vanes. The gas-tightness of sinter vanes is improved by sealing residual cells in metal oxides and matrices containing dispersed metal oxides created through water vapor treatment. However, the cells are not completely sealed by the water vapor treatment, so escape of lubricant due to the open cell nature of the open cells.